Inflammation may also increase with older age. Inflammation can be described as the body’s usual response to injury or infection. For example, if a person injures a finger, the finger will become swollen, red, and painful. The swollen, red, and painful feelings are a result of inflammation, caused by several chemicals that the body’s defense system releases. These chemicals, called inflammatory mediators, are released by several types of blood cells. As scientists have learned more about inflammation, they have found that the body often produces inflammatory mediators without any clear evidence of injury to the body. When inflammatory mediator levels remain high in the bloodstream over a long period of time, they appear to produce changes in the blood vessels. More recent research suggests that inflammation is an important risk factor for heart attack and increasing evidence suggests that inflammation affects the brain as well.
Inflammatory mediators in the bloodstream can affect the brain directly, and may also cause the brain to stimulate the release of hormones. One example of this occurs when these mediators affect the part of the brain that sends out signals to the adrenal gland to make hormones such as cortisol. Cortisol is a stress hormone that has been associated with depression. Previous studies of depression have shown that increased inflammatory mediators are associated with increased depression. A group of researchers decided to examine several inflammatory mediators in the elderly to determine if there was a connection between inflammation and depression in this age group.
What the researchers did
The researchers surveyed several thousand people aged 70-79 and asked them questions about their levels of depression. They also recorded data for other variables such as medical illnesses and medications the people were taking. The researchers then examined the relationship between three different inflammatory markers and rates of depressive symptoms. Depressive symptoms were studied using questionnaires so the method was a little different than if psychiatrists had interviewed each person. The researchers tried to rule out or control for influences of medical problems or medications.
What the researchers found
The researchers discovered that high levels of inflammation were associated with higher levels of depression. They found that having high levels of two of the inflammatory mediators was associated with more depression than having high levels of one inflammatory mediator. In the people who had high levels of at least two inflammatory markers, the rates of depression were about two and one-half times higher.
Overall, this is an interesting, well-designed, and important study that links inflammation to depression in the elderly. One important limitation to this study is that it doesn’t prove that inflammation causes depression. It may be the other way around. Changes in the brain associated with depression might cause inflammation, leading to an association between depression and increased inflammatory markers. But, it’s my opinion that inflammation leads to changes in the blood vessels and the brain that increase the risk for depression. As always, more research is needed to better understand inflammation’s role in depression. Because inflammation is also associated with cardiovascular disease and because cardiovascular disease and depression are linked as well, it’s important that we learn more about this problem. This line of research creates the possibility that future treatments that lower inflammation in the body might help prevent both heart disease and depression—a welcome development in our fight against these serious illnesses.
Penninx B.W.J.H., Kritchevsky S.B., Yaffe K, Newman A. B., Simonsick E.M., Rubin S., Ferrucci L., Harris T., Pahor M. Inflammatory markers and depressed mood in older persons: results from the health, aging and body composition study. Biological Psychiatry 2003, volume 54, pages 566-572.